The invention concerns an extruded molding from powdered materials, of solid or hollow cross-section, and a process for its manufacture.
The extrusion of sintered powder blanks by means of a ram to form given types of moldings is a well-known process in powder metallurgy. In addition to other factors, for example, the dimensions of the ram and the die, matching of the ram pressure and the friction occurring during extrusion is of particular importance. To minimize the friction as far as possible, lubricants such as paraffin, molybdenum sulphite or glass are used. Powdered glass in particular, however, imparts a rough surface to a hot-extruded molding because of the glass deposits left upon it, with the result that the molding generally required further processing. The use of powdered glass as a lubricant is also unsatisfactory in terms of dimensional accuracy and causes relatively high eccentricity of the extruded molding.
Although the friction occurring in conventional extrusion processes, particularly "wall friction" is reduced to a certain extent by the lubricants specified, the remaining frictional resistance can, in certain cases, be so high as to place limitations on the length of the extruded blank. This applies particularly to the extrusion of tubing of relatively small internal diameter.
The task of the present invention is therefore to produce from powdered materials a molding relatively long in relation to its cross-section and of relatively high density and dimensional accuracy, while having a gas and liquid-tight and smooth external and/or internal layer. It is a further objective to provide an economical process by means of which a molding of this type can be easily manufactured.